Conventionally, when machining is performed by a laser machining apparatus, selection of a machining condition on the basis of an instruction from an NC (Numerical Control) apparatus and setting of a machining object (workpiece) are separately performed, therefore there is no correlation between them. Thus, even if the machining condition does not correspond to the machining object, machining is performed, which results in a machining defect.
As a method of determining whether a desired machining object is set, there is a method of arranging a reflected light detection sensor above a machining object and measuring the reflected light by this reflected light detection sensor. For example, when laser light is obliquely incident on the surface of the machining object, the reflected light intensity that can be detected depends largely on the angle due to the arrangement position of the reflected light detection sensor except for the case where the incidence angle of the laser light is always determined. In order to avoid this, a strip-shaped sensor needs to be arranged in a doughnut pattern to surround the optical axis of the incident laser light, therefore, the apparatus becomes complicated. Moreover, there is a method of arranging the reflected light detection sensor at a position spaced apart from the optical axis and causing laser light to be vertically incident on the surface of the machining object (for example, see Patent Literature 1).